Replacements for the self-interest axiom may posit weak to strong theories of sociality. Strong sociality may be useful for positing social cognitive mechanisms and their evolution, but weak sociality may work better for identifying interesting group-level outcomes by focusing on deviations from self-interested psychological assumptions. Such theoretical differences are likely to be based on disciplinary expertise, and the challenge for Darwinian integration is to keep the conversation flowing.

A single evolved psychological mechanism, social identity, may help explain the development of salient sex differences in aggression. Bearing children automatically provides a basis for positive social identity for females. Masculine identity is more problematic, especially where the range of possible cultural roles is small. Ethnohistorical data provides insight into the overlap between masculine values and warrior values.